Stan said 
"I am having problems this year with Black Queen Cell Virus in my queen
raising hives.  Mite levels are a bit higher than normal in my whole
operation for this time of year.  Perhaps nosema levels are higher
too, since hives being buried in the snow all winter was conducive to
nosema buildup."

I too have seen this problem here in Western Australia in the past. In my case I am sure it was Nosema related even though no clinical signs of Nosema were evident. (Nosema apis is always lurking the background here, and we do not have Nosema ceranae.) On one occasion I was losing hundreds of the cells to BQCV and I attributed it to my cell starter colonies having wintered on a site with too much shade....a classic situation to favour, perhaps even encourage, Nosema prevalence. It was an unintentional failure due to my own problematic health situation at that time. I tried to salvage the situation by purchasing queen cells from another queen producer, only to experience exactly the same problem! Her cell builder colonies had definitely overwintered in a full sun site, on ostensibly good nutrition. (Our climate is such that the bees can fly every day, and good pollen sources are continuously available throughout autumn, winter and spring....and of course, no snow!). However, it had been an unusually wet spring, even more so in her location 200km north of me.
So Stan, my money is on Nosema, and as you know, there is not much you can reasonably do about that, other than tough it out. In our case the problem resolves itself, BQCV disappearing  as the spring warms up and the season progresses.
My take home message was to resist the temptation to commence queen rearing too early in the spring in my location, and it has become standard practice for me now.

PeterD
in Western Australia where spring flora are well under way despite what we call winter (cold weather) arriving at the time it should have been leaving!

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html